.px2rem(@name, @px){
    @{name}: @px / 75 * 1rem;
}
.header{
    width: 100%;
}
.nav{
    .px2rem(height, 76);
    .px2rem(margin-top, 2);
    .px2rem(font-size, 24);
    .px2rem(line-height, 28);
    display: flex;
    li{
        flex: 1;
        display: flex;
        align-items: center;
        text-align: center;
        justify-content: center;
    }
    .on{
        background: #df3434;
        color: white;
    }
}
.up{
    width:0;
    height:0;
    border-width:30px 30px 0;
    border-style:solid;
    border-color:#333 transparent transparent;/*灰 透明 透明 */
    margin:40px auto;
    position:relative;
}